The structure and function of aviation plug thermocouple

Thermocouple (Temperature Measurement)
Principle: Utilizes the thermoelectric effect (Seebeck effect) generated by temperature changes between two dissimilar metals (such as K-type nickel-chromium-nickel-silicon) to generate a mV-range voltage signal.
Temperature Measurement Range:
Type K: -200°C to 1200°C (commonly used in food processing machinery, such as vacuum packaging machine heat seal head temperature measurement).
Type J: 0°C to 760°C (iron-copper-nickel alloy, suitable for medium to low temperatures).
Sheath Material: Stainless steel (such as 304/316) or ceramic (for high-temperature environments); corrosion and wear resistance are required.
Aircraft Plug (Connection)
Purpose: Provides a quick-connect, dust-proof, waterproof, and anti-interference electrical connection.
Features:
Metal housing (usually nickel-plated copper) with a threaded locking mechanism to prevent vibration and disengagement.
Ingress Protection: IP65/IP67 (dustproof and waterproof).
Number of Pins: 2-core (thermocouple), 4-core (with compensation wire), etc. II. Common Problems and Troubleshooting
1. Abnormal Temperature Display (e.g., jumping, no signal)
Possible Causes:
Broken thermocouple wire or damaged sheath.
Poor contact in the aviation plug (oxidized, loose).
Reverse polarity or short circuit in the compensation wire.
Troubleshooting Steps:
Measure Resistance: Disconnect the plug and use a multimeter to measure the resistance across the thermocouple. Normally, it should be several ohms (if it's open, it's damaged).
Check the plug: Clean the pins/socket to ensure there's no oxidation or deformation, then re-tighten it.
Verify the Signal: Briefly heat the thermocouple tip with a lighter and observe whether the temperature controller's reading increases (if there's no change, the thermocouple is faulty).
2. Overheating or Corrosion in the Aviation Plug
Causes:
Insufficient current carrying capacity in the plug (e.g., high current flowing through a small plug).
Excessive contact resistance (oxidized or loose pins).
Solution: Replace the aviation plug with one with a higher current rating (e.g., 10A or higher) and ensure it's securely plugged in. 3. Sealing failure (water/dust ingress)
Handling:
Check the plug O-ring for aging and replace with a high-temperature-resistant silicone seal.
Apply a small amount of sealant (such as Loctite 243) when tightening the threads.
III. Key Points for Selection and Replacement
Matching Parameters
Thermocouple: Type (K/J/T, etc.), temperature range, sheath diameter, and length (must match the heater tube mounting hole).
Aviation Plug: Number of pins, pin material (gold/silver plated), IP rating, and temperature rating (e.g., -40°C to 200°C).
Installation Precautions
The temperature measuring end of the thermocouple must be in close contact with the heater tube or heat-sealing mold surface (thermal grease can be used to enhance contact).
When wiring the aviation plug, pay attention to the polarity of the compensation wire (positive and negative poles cannot be reversed).
Recommended Brands
Thermocouples: Domestic (Shangzi Instrument, Sichuan Instrument), Imported (Omron, Honeywell).
Aviation Plugs: JAE (Japan Aviation Electronics), Amphenol (Amphenol), Domestic (Aerospace Electric). IV. Maintenance Recommendations
Regular Inspection: Clean the plug contacts monthly and inspect the thermocouple sheath for damage.
Calibration: Calibrate the thermocouple signal error annually using a standard temperature source (such as a dry-well furnace).
Replacement Period: 1-3 years in normal environments; shorter periods are required in high-temperature and high-humidity environments.